Vapor-compression type refrigeration systems are commonly used in transport refrigeration systems, such as temperature controlled trucks or trailers. Some vapor-compression refrigeration systems can switch between a cooling cycle and a heating (and/or defrost) cycle. Such systems may also be called heat pumps.
In some heat pumps, a receiver may be positioned in-line within a refrigerant line between a condenser and an evaporator. In a cooling cycle, the receiver can store liquid refrigerant coming out from the condenser before the refrigerant is driven into the evaporator through a throttle device. In a heating cycle, the receiver may not be necessary and can be by-passed.
In some heat pumps, an accumulator may also be positioned in-line within the refrigerant line between the evaporator and the compressor. In a cooling cycle, the accumulator can trap, for example, liquid refrigerant contained in the refrigerant gas before the refrigerant gas going into the compressor. During a heating and/or defrost cycle, the accumulator may also function as a reservoir to retain liquid refrigerant. Compressor lubrication oil contained in the refrigerant gas may also accumulate in the accumulator before the oil returning to the crankcase of the compressor. Both the receiver and the accumulator generally have an internal reservoir to contain liquids.